A10.0-ml sample of 0.200 m hydrocyanic acid (hcn) is titrated with 0.0998 m naoh. what is the ph at the equivalence point?

Question

A10.0-ml sample of 0.200 m hydrocyanic acid (hcn) is titrated with 0.0998 m naoh. what is the ph at the equivalence point? for hydrocyanic acid, pka = 9.31

Hermina Ferry · Accepted Answer

When the titration of HCN with NaOH is:HCN (aq) + OH- (aq) → CN-(aq) + H2O(l)So we can see that the molar ratio between HCN: OH-: CN- is 1:1 :1we need to get number of mmol of HCN = molarity * volume                        = 0.2 mmol / mL* 10 mL = 2 mmolso the number of mmol of NaOH = 2 mmol according to the molar ratioso, the volume of NaOH = moles/molarity                                          = 2 mmol / 0.0998mL                                          = 20 mL and according to the molar ratio so, moles of CN- = 2 mmol∴the molarity of CN- =  moles / total volume                                    = 2 mmol / (10mL + 20mL ) = 0.0662 Mwhen we have the value of PKa = 9.31 and we need to get Pkbso, Pkb= 14 - Pka            = 14 - 9.31 = 4.69 when Pkb = -㏒Kb         4.69 = -㏒ Kb ∴ Kb = 2 x 10^-5and when the dissociation reaction of CN- is:CN-(aq) + H2O(l) ↔ HCN(aq) + OH- (aq) by using the ICE table:∴ the initials concentration are:[CN-] = 0.0662 Mand [HCN] = [OH]- = 0 Mand the equilibrium concentrations are:[CN-] = (0.0662- X)[HCN] = [OH-]= Xwhen Kb expression = [HCN][OH-] /[CN-]by substitution:2 x 10^-5 = X^2 / (0.0662 - X)X = 0.00114 ∴[OH-] = X = 0.00114when POH = -㏒[OH]                    = -㏒ 0.00114 POH = 2.94∴PH = 14 - 2.94 = 11.06

Hermina Ferry · Answer

answer: the rate of diffusion increases with increase in temperature.increase in temperature, increases the molecular/particles speed (kinetic energy. diffusion means movement of particles through the material. generally, the heavier the particle the more it interacts with the environment and more the temperature matters. so higher temperature results in higher diffusion.

Hermina Ferry · Answer

the correct answer is b. a strong acid completely dissociates to its ions when dissolved in water. completely dissociates to and ions. a is incorrect because does not fully ionize to and ions and some remain as the compound . c and d are incorrect because, and do not fall into the category of bronsted lowry acids. a bronsted lowry acid is a proton donor and since both molecules do not have a proton to donate they are not bronsted lowry acids. likewise,   if we use the lewis acid definition, they cannot be acids. a lewis acid is an electron pair acceptor. both and have a complete octet so can not accept any electrons which disqualifies them as acids.

Jakob Littel

A10.0-ml sample of 0.200 m hydrocyanic acid (hcn) is titrated with 0.0998 m naoh. what is the ph at the equivalence point?

3 Answers

AI-Powered Insights

Want to answer this question?

Categories

Tags

Related Questions